Electrical connectors of the type to which the present invention relates are shown in U.S. Pat. Nos. 4,684,196 and 4,427,253 and in German Patent No. DT 29030960. The purpose of these connectors is to form an electrical and mechanical joint between two conductors which are often of differing sizes, and which are formed of either solid wire or, more often, stranded wire bundles. The conductors are usually also covered with an insulated sheath. Quite commonly the connection to be made between the two conductors by such clamps is made by way of a tap connection, that is, by connecting the supply end of one conductor to a point along the length of another conductor which is often of larger diameter. In some applications, the connections are made when the conductors are live.
The electrical connection of these connectors is provided by one or more bridging members of electrically conductive material usually having insulation piercing teeth formed at each end of the bridging member which are able to pierce any insulation covering the conductors to form an electrical contact with the conductive wire strands. The teeth enable the formation of an electrical connection between the insulated conductors without the need to remove the insulation. The electrical connecting bridging members of the clamp connector are usually encased in and surrounded by an insulating body formed of molded insulating material The insulating body is typically formed of a pair of mating body halves which are bolted together by a bolt which passes through the insulated halves to compress them together. The assembled halves clamp the conductors therebetween driving the insulation piercing teeth into the conductors to form the electrical connection as well as a mechanical connection as the bolt is tightened.
In the design and manufacture of connectors of this type, it has been desirable to maintain an insulated barrier to protect persons installing the conductors and others working in the vicinity of these connectors and the energized conductive elements. The bridging members of these connectors are necessarily fabricated of conductive material while the remaining portion of the clamp is predominately of insulating material. It does, however, remain necessary to join the two body halves together with a steel or other strong metallic bolt in order to obtain sufficient clamping strength between the body halves. To transmit the clamping force from the bolt to the more fragile insulated material, a stress distributing plate, also of steel, is typically provided between the bolt head on one of the insulated body halves of the cap portion of the body through which the bolt is inserted. A threaded stress distributing nut or embedded plate is typically provided on the other body half or base portion to engage the nut and to distribute the stress at the insulated base portion.
To effectively insulate the conductors and bridging members, the insulating bodies of clamp connectors are provided with an insulating cylindrical chimney-like column which extends the bolt hole of one body half. The chimney interfits in a cavity around the bolt hole of the other half. The chimney insulates the bolt from the conductors, preventing the conductor strands from contacting the bolt while the clamp is being tightened. This is important both when uninsulated conductors are used and to prevent the insulation sheath on insulated conductors from being cut if deformed against the bolt during tightening.
The need to provide sufficient strength to affect the clamping action between the two clamping halves of the connector body has resulted in the use of the threaded metallic nut or a plate to receive the free end of the bolt to affect the clamping action. Some prior art devices have employed a metal threaded nut or plate at the external lower surface of the lower insulated body half to tighten on the lower bolt end. This arrangement has resulted in a protrusion of the bolt end from the lower portion of the clamp as is more particularly shown in U.S. Pat. No. 4,427,253 and German Patent DT 2903960. The protruding bolt end has had a tendency to snag on the surfaces of objects into which the conductor cables come into contact. Such a problem was overcome in U.S. Pat. No. 4,684,196 with the use of an embedded threaded plate in the lower clamp portion for tightening upon the bolt end.
The prior art clamps of both the protruding bolt and imbedded plate designs have relied heavily on the threaded metallic nut or plate to provide an adequately strong connection with the bolt so as to exert enough compressive force between the two portions of the clamp body to make an effective electrical and mechanical connection. The provision for threads in the insulative material has been introduced as shown in U.S. Pat. No. 4,684,196 to guide the bolt into proper alignment with the threads of an embedded plate and to provide some auxiliary clamping force as a result of the threaded engagement between the bolt and the lower body half. The threads formed in the lower body half have run continuously from the chimney portion through the body half and the embedded plate.
The distribution of the stress from the bolt to the insulative material of the lower clamp half by direct engagement with threads in the insulative material has resulted in the prior art in breakage of the insulative material of the clamp body. Such breakage has been experienced particularly to the chimney portion. The extended threads through the length of the bolt hole has been ineffective to avoid this problem. In the prior art, the use of the threaded metallic nut or embedded plate has been relied upon to tighten the bolt and provide the compressive force needed for the clamping action. The use of the plate, particularly when embedded in the insulative material, has also contributed to the cost of the fabrication of the clamps employing them.
Accordingly, there has existed in the prior art a need for a more effective and efficient structure for joining the two members of electrical clamps together.